Also, make sure you've got the prop tight. The nut holding the propeller tight on the engine also holds the spinner tight. The front of the spinner just holds onto the backplate. When everything comes off, it's because the prop nut isn't tightened enough to hold everything on. If just the front of the spinner was loose only that would come off.

Sometimes the spinner backplates don't give the engine's thrust washer (the part with the gripping teeth) something to grab hold of. Sometimes just a little extra tightening of the prop nut can do the job, sometimes not. But for sure, it everything is coming off, it's because the prop nut wasn't tight enough.